Spintronic THz Wave Emitter: an approach from Topological Weyl Semimetal Heusler alloys

为了实现研究目标，我研究了Weyl-Heusler合金Co2 MnGa的太赫兹辐射。我已经获得了系统的数据，在太赫兹发射的Co2 MnGa与不同的化学顺序。根据过去的研究，认为在单层铁磁体（非Weyl半金属）中，由于基底或覆盖层的背散射，铁磁层内部的激光激发电子产生回流电流，该回流电流由于反常霍尔效应（AHE）而发射THz波。这种背散射过程强烈依赖于结构特性，如厚度，粗糙度，等，因此，我还专注于从Co2 MnGa薄膜的太赫兹发射的厚度依赖性，以深入了解通过AHE的背散射诱导的太赫兹发射的机制。对于薄制度的Co2 MnGa薄膜上生长的MgO衬底和覆盖的MgO层，我发现了强烈的签名，太赫兹发射的起源是AHE，这是增强的外尔性质的Co2 MnGa。此外，我已经研究了Co2 MnGa的太赫兹发射的成分依赖性，以澄清如何相对于费米能级的怀尔点位置的影响太赫兹发射。这些结果在几次会议上进行了讨论，并提交了该文件。

To achieve the research objectives, I investigated the THz emission from Weyl Heusler alloys Co2MnGa. I have obtained systematic data for the THz emission in Co2MnGa with different chemical ordering. According to the past research it was believed that in a single layer ferromagnet (not Weyl semimetals) the laser-excited electrons inside the ferromagnetic layer generates a back-flow current due to back scattering from substrate or capping layer which emits a THz wave due to anomalous Hall effect (AHE). Such back-scattering process strongly depends on the structural properties like thickness, roughness, and etc. Thus, I also focused on thickness dependence of the THz emission from Co2MnGa films to gain insight into the mechanism of the back scattering-induced THz emission via AHE. For thin regime of Co2MnGa films grown on MgO substrates and capped by the MgO layers, I found the strong signature that the origin of the THz emission was AHE which was enhanced by Weyl nature in Co2MnGa. In addition, I have investigated the composition dependence of the THz emission of Co2MnGa to clarify how the Wyle point location with respect to the Fermi level influences the THz emission. Those results were discussed in several conference meetings and the paper was submitted.